In IEEE802.15 Task Group 3c, studies are underway for the physical layer of a high-rate wireless personal area network (“WPAN”) using millimeter wavebands around the 60 GHz band. Examples of an application applied the millimeter-wave WPAN are data transfer at a very high data rate over 2 Gbps such as high speed internet access, video streaming (e.g., video on demand, HDTV meaning high definition television, and home theater), and wireless data bus instead of a cable.
Various modulation schemes are considered such as BPSK, QPSK, OOK and OFDM for utilizing the millimeter-wave WPAN. In millimeter-wave utilization by a portable device such as kiosk file downloading, the device is preferable which has a small circuit scale and which adopts a single carrier communication scheme such as BPSK, QPSK and OOK that are suitable for low power consumption and low cost. Therefore, the kiosk side apparatus needs to be realized such that the apparatus can communicate with a portable device in phase modulation scheme such as BPSK and QPSK, and a portable device in amplitude modulation scheme such as OOK.
FIG. 1 is a block diagram showing the main components of QPSK/OOK modulation apparatus 10 according to the first prior art (see Patent Document 1 and Patent Document 2). As shown in FIG. 1, QPSK/OOK modulation apparatus 10 is provided with: OOK data generating section 12 for generating OOK transmission data; QPSK data generating section 13 for generating QPSK transmission data; two pulse shaping sections 14-1 and 14-2 for shaping pulse waveforms of OOK or QPSK data to meet spectral mask; two low pass filters (“LPFs”) 16-1 and 16-2 for removing harmonic components from OOK or QPSK data having passed through pulse shaping sections 14-1 and 14-2; filter property switching section 15 for switching between the filter properties of pulse shaping sections 14-1 and 14-2 in association with OOK data or QPSK data; QPSK modulating section 17 for performing QPSK modulation for OOK data or QPSK data from LPFs 16-1 and 16-2; and a modulation selecting section 11 for controlling OOK data generating section 12, QPSK data generating section 13 and filter property switching section 15 according to modulation indication signal S11.
QPSK modulating section 17 is provided with two mixers 17-1 and 17-2 connected respectively to the outputs of LPF's 16-1 and 16-2, and summer 17-5 for adding signals outputted from mixers 17-1 and 17-2. Mixer 17-1 is directly connected to a carrier wave generated by oscillator 17-3, while mixer 17-2 is indirectly connected to a carrier wave via 90-degree phase sifter 17-4.
In FIG. 1, when modulation indication signal S11 indicates the OOK modulation, modulation selecting section 11 activates OOK data generating section 12 and deactivates QPSK data generating section 13. Modulation selecting section 11 also commands filter property switching section 15 to switch the filter properties of pulse shaping sections 14-1 and 14-2 for OOK data.
OOK data generating section 12 outputs 40 signal S12 and Q(t) signal S13, which are represented by equations 1 and 2.(Equation 1)I(t)=αD(t)  [1](Equation 2)Q(t)=0  [2]
Here, α is a constant, and D(t) is an input data signal taking one of a “0” value and a “1” value. Output RF signal S14 of QPSK/OOK modulation apparatus 10 is represented as shown in equation 3.
                    (                  Equation          ⁢                                          ⁢          3                )                                                                                                                S                ⁡                                  (                  t                  )                                            =                                                I                  ⁢                                      (                    t                    )                                    ⁢                  sin                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                                      Q                    ⁡                                          (                      t                      )                                                        ⁢                  cos                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                                                                                        =                              α                ⁢                                                                  ⁢                                  D                  ⁡                                      (                    t                    )                                                  ⁢                sin                ⁢                                                                  ⁢                ω                ⁢                                                                  ⁢                t                                                                        [        3        ]            
As known from equation 3, output RF signal S14 is in the form of an OOK modulation wave.
FIG. 2 is a block diagram showing the main components of QPSK/OOK modulation apparatus 20 according to the second prior art (see Patent Document 1 and Patent Document 3). Unlike QPSK/OOK modulation apparatus 10 shown in FIG. 1, QPSK/OOK modulation apparatus 20 employs a configuration eliminating filter property switching section 15 and adding amplitude modulating section 28 for amplifying output signal S24 of QPSK modulating section 26. Further, QPSK/OOK modulation apparatus 20 adopts a different method of generating an OOK modulation wave.
In FIG. 2, when modulation indication signal 21 indicates OOK modulation, as generally well known, OOK data generating section 22 outputs I(t) signal S22 and Q(t) signal S23, which are represented by equations 4 and 5.(Equation 4)I(t)=cos φD(t)  [4](Equation 5)Q(t)=sin φD(t)  [5]
Here, φ is a constant (e.g. 45 degrees). As shown in equations 4 and 5, methods of generating a 90-degree phase difference signal include assigning a phase difference to an IF (Intermediate Frequency) signal generated using a local oscillator of lower frequencies than radio frequencies, adjusting a phase by varying the generation timing of rectangular waves, and so on. Further, note that I(t) signal S22 and Q(t) signal S23 represented by equations 4 and 5 differ from I(t) signal S12 and Q(t) signal S13 represented by equations 1 and 2. Based on equations 4 and 5, output signal S24 of QPSK/OOK modulation apparatus 20 is represented by equation 6.
                    (                  Equation          ⁢                                          ⁢          6                )                                                                                                                S                ⁡                                  (                  t                  )                                            =                              α                ⁡                                  (                                                                                    I                        ⁡                                                  (                          t                          )                                                                    ⁢                      sin                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      t                                        +                                                                  Q                        ⁡                                                  (                          t                          )                                                                    ⁢                      cos                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      t                                                        )                                                                                                        =                              α                ⁢                                                                  ⁢                                  D                  ⁡                                      (                    t                    )                                                  ⁢                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                  ⁢                        t                                            +                      ϕ                                        )                                                                                                          [        6        ]            
As known from equation 6, output RF signal S24 is also in the form of an OOK modulation wave.
QPSK/OOK modulation apparatus 20 shown in FIG. 2 has an advantage over QPSK/OOK modulation apparatus 10 shown in FIG. 1 in terms of operational stability. This is because QPSK/OOK modulation apparatus 20 utilizes both I (i.e. in-phase component) and Q (i.e. quadrature component) branches to implement OOK modulation, both I and Q branches operate in synchronization with each other so that variations in the ground levels or the like are corrected or cancelled out with each other, and amplitude modulating section 28 performs amplitude modulation. However, a disadvantage of QPSK/OOK modulation apparatus 20 is that it additionally requires amplitude modulating section 28, resulting in increased implementation complexity.    Patent Document 1: U.S. Patent Application Laid-Open No. 2003-157888, specification    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-147052    Patent Document 3: U.S. Patent Application No. 7120202, specification